You are looking for a DD. What do you know about your engine? Is it stock compression, stock cam and heads?

An easy slight HP gain for it would be an aftermarket 180° dual-plane intake manifold (we use a Weiand Street Warrior 8120 WND) and we chose a Holley 650 double-pump carb with mechanical secondaries (because we have a manual transmission) HLY-0-4777S. The carb is a bit large for a stock cam, so you could go to a 500 or 600 CFM carb if you choose.

These should all be bolt-on improvements. We bought through Summit Racing.

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1970 GMC K2500
Dis-use is harder on a car than mis-use.